Does this count?
I am SLF but when in the RAF I used to Hitchhike in uniform to and from Airshows.
One occasion in the 60s I managed a lift out of Coltishall after an Airshow.
Making may way home to the West country where I was then Stationed
It is still very sensitive so I will generalise on some aspects.
The A/C was an Argosy, static at the show but on return to the UK from a
Training stint around the Med.
Come the time to depart after the show as was the "practice"!!!! along with other departing aircraft the Pilot decides to show off with a max rate steep climb out .
Not a good idea as strapped down in the back, nexr to where I was seated was the Pilots private Car!!!!!!!!!. Road ready!!!!!
Very very much against Regs., the crew used it to run around at the ports of call.
So max tatical take off .steep angle, , pressure differences, result......
Petrol from the fuel tank overflows via the filler overflow outlet.
I then informed the loadmaster of Petrol swilling around the Cargo floor. ,and the smell of Petrol fumes filling the hold.
I had never seen someone go pure white with fright until then.
Talk about Panic. Full emergency routines inside the Aircraft, absolute minimum electrics etc..Unable to declare to ATC the "Situation"
So there was your truely .an undeclared passenger not on the Manifest.
sitting in a flying "Bomb" ,to say I was cra**ing myself was an understatement.
The hairiest moment I felt was on deployng the Landing gear, as I imagined sparks/static or what ,could blow us to hell and back.
Suffice to say we landed ok and the Loadmaster took me to one side and
forcibly told me that there never was a "Situation" and on pain of death to
keep quiet about it for years to come.
45 years have now passed so I feel I am safe to relate this tale.